systemd: needs kernel headers >= 3.8

Systemd needs Linux headers >= 3.8 because it uses IFLA_GRE_FLOWINFO,
IFLA_IPTUN_FLAGS from linux/if_tunnel.h.

Fixes http://autobuild.buildroot.org/results/ad3/ad3b4003dc50582a493f1156234d83652104a6bf/

Signed-off-by: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

system/Config.in

@@ -96,12 +96,12 @@ config BR2_INIT_SYSTEMD
 	depends on BR2_TOOLCHAIN_HAS_SSP
 	depends on BR2_USE_MMU
 	depends on !BR2_PREFER_STATIC_LIB
-	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_0
+	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_8
 	select BR2_PACKAGE_SYSTEMD
 
-comment 'systemd needs an (e)glibc toolchain, headers >= 3.0'
+comment 'systemd needs an (e)glibc toolchain, headers >= 3.8'
 	depends on !(BR2_TOOLCHAIN_USES_GLIBC \
-		&& BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_0)
+		&& BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_8)
 
 config BR2_INIT_NONE
 	bool "None"